Digitally operable pumps with thermoplastic check valves are presently known in the relevant art for a variety of applications. One such pump is disclosed in my prior U.S. Pat. No. 5,144,708 (the '708 Patent) which is commonly used to inflate elastomeric bladders. As shown, an air inlet in the form of an outwardly facing air hole 22 is provided through an outer wall of a pump 28. The pump is operated by alternately compressing and releasing the outer wall of a pump chamber, filled with an open cell elastomeric material 14 and which, upon release of the compression force, is capable of expansion. For proper use of this type of digitally operable pump 28, it is necessary to cover the air hole 22 using one's thumb or finger during each compression stroke and to uncover the hole during each intake stroke whereby air will be alternately forced from the pump chamber into the bladder 30 and drawn through intake hole 22 during each expansion stroke. In normal operation, air cannot escape from the pump chamber through the intake hole 22 during compression because the user's thumb serves to seal the intake hole.
While pumps of such a configuration perform adequately in many applications, for other applications they have been found to have certain limitations. One such limitation relates to the fact that for each pump stroke, the inlet hole 22 must be controlled digitally and the pump will only operate properly if an air tight seal is formed over the inlet hole 22 during application of compressive force to the pump. Although this is normally not a daunting task, it may be more difficult to accomplish if the user is wearing gloves, such as is likely in cold weather conditions. Under such conditions, the user may find it awkward to use the pump while wearing gloves or uncomfortable to do so without gloves. The outwardly facing disposition of the air intake hole 22 has also been found unsuitable in cold weather applications, such as in inflatable ski boot liners when the ambient temperatures of the air out of door are frequently well below freezing. In such conditions, inflating the boot liner by pumping such cold air directly into one's boot liners will invariably result in chilling the wearer's feet at the start of a day of skiing.
Another drawback in the use of such pumps will occasionally occur when used in wet, slushy or dirty conditions in which wet, slushy snow or water may clog the inlet hole or enter the pump chamber through the exposed inlet hole so as to adversely affect the operation of the pump.
One solution to the problems associated with pumps such as those disclosed in my '708 Patent, is to relocate the air inlet opening and utilize an inlet check valve rather than an outwardly exposed inlet hole. In that connection, my U.S. Pat. No. 5,074,765 discloses a check valve 20 for use with a hand-operated pump for an inflatable bladder. The valve 20 is of a "flapper" type comprising a flexible portion or an elastically resilient dome 8 which operates in response to differential air pressure within and without the pump chamber. The valve is intended to prevent fluid, such as air from flowing out of the chamber during each compression stroke but will swing "open" to allow air to enter the chamber on the expansion stroke. The principal drawback of this valve construction is its relatively high manufacturing costs resulting from the material requirements of the structural strength and recovery resilience for effective operation of the pump dome. In addition, the construction of the valve 20 which is an integral part of the pump dome has been found less than totally satisfactory in sealing the pump chamber during compression of the dome.